Davis: Anatomy and Physiology, the Heart Part 2

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Rhythmicity

maintains steady and regular rhythm which is a steady cycle of contraction and relaxation. a. Occurs from birth to deathb. Average Heart Rate (HR) of healthy adult is 75BPMc. Women usually 72-80BPM at restd. Men usually 62-72BMP at reste. Metabolic rate, heart size, physical exercise affect HRf. Humans (Vertebrates) contain a Myogenic Pulse

Myogenic Pulse

the ability for the heart to create its own electrical impulse.

Pacemaker of the Heart

path of tissue that generates electrical impulse that is independent from the rest of the body's NS. a. Receives sympathetic innervation by Cardiac Nerves that originate in the cervical gangliab. Receives Parasympathetic innervation by the Vagus Nerve (CN-X) which sends branches to the Pacemaker to slow down pulse rate constantly.c. Electrocardiogram (ECG or EKG) measures heart rated. It is autorhythmic (self-stimulating) eventhough the brain can tell the heart to heat harder or slower.

Cardiac Cycle

controls routes and timing of electrical conductioni. Beats in sequence, whole heart does not beat at the same time. ii. Regulates flow of electricity in correct order, order of circulationiii. Sinoatrial Nodev. Atrioventricular Node: (AV Node) forks to vi. Atriovenricular Bundles split into vii. Purkinje Fibers that attach to some viii. Cardiocytes:

Sinoatrial Node (SA Node)

(SA Node) pacemaker of heart, small path of modified myocytes found in rt. Atrium, near the opening of Vena Cava1. produces an regular electrical stimulus, a constant AP to allow blood to move through the system2. sends signals to rt and left atrium3. Produces regular electrical stimulus4. Travels to rt atrium then to left atrium

Atrioventricular Node (AV Node)

located near right AV valve and found at inferior end of atrioventricular septum1. Functionsa. Transfers signal from atria (of SA node) to ventriclesb. Slightly delays the signal to give time for ventricles to fill upc. Transfers signal from atria (of SA node) to ventriclesd. Slightly delays the signal to give time for ventricles to fill up2. Gateway to allow the heart to get electrical impulse from top to bottom because of non-conductive fibrous skeleton

Atrioventricular Bundles (Bundle of His)

found in the ventricles where the AV node forks and distributes to Rt and Left Ventricles. a. Right bundles go to rt. Atriumb. Left bundles go to left atrium, purkinje fibers are more elaborate in order to produce a more forceful charge.

Purkinje Fibers

small nerves that distribute electrical signals to myocytes/Cardiocytes of ventricles. Extends from Bundle of His.

Cardiocytes/Myosytes

cells of the heart1. Mono-nucleated2. Thick3. Y-shaped4. Joined to others end to end5. Can directly stimulate to each other by intercalated disksa. contains Gap Junctions: provide a place for an electrical signal to cause a contraction6. Cells contract in a wrapped sequence7. Contains much more mitochondria and is much larger - for its need to be constantly working8. runs on aerobic respiration9. Fuel Use:a. 60%-Fatty Acidsb. 35%- Glucosec. 5%- proteins and other molecules 10. Contains many Myoglobins: storage for O2 11. Contractions are usually long and slow, and will not experience swift twitch a. Absolute Refractory Period is 200-250 msec.b. Prevents summation of tetanic. Provides sustained pressure to squeeze blood out of ventricles.12. Highly resistant to tetanus13. Requires a lot of O2, energy, and nutrients to keep the cells running - "expensive"14. Non-mitotic15. Damage will be healed by fibrosis (scar tissue)16. Contains a small amt. of Satellite Cells: stem cells that decrease as age increases

Ectopic Focus

any part of the heart other than the SA node that fires an electrical impulse.

Premature Ventricular Contractions (PVC)

aka extrasystolea. Extra contraction b. Not as forceful as normal rhythmc. Usually originates from AV node - causing a Nodal Rhythmi. Cardiocytes can generate their own pulse but it's even slower (20-40BPM)

Nodal Rhythm

which produces a slower pulse (40-50BPM) that is not enough to maintain function

Systole

contraction of the heart

Diastole

relaxation of the heart

Sinus Rhythm

SA Node contains no stable electrical chargea. Usually beats at 100bpm but Vagus Nerve will slow the heart to 75bpmb. Runs on Pacemaker Potential:

Pacemaker Potential

i. At -60mv charge begins to increaseii. When it is reached to -40mv, stimulates gated ion channels to open and Ca2+ rushes into cardiocytes causing an increase of electrical charge (depolarization)iii. When the membrane potential reaches >0mv, Pacemaker Potential becomes +, stimulates other channels to open rushing K+ out of cardiocytes (repolarization), charge will reach to -60mv again.iv. It takes .8sec for 1 AP to occur causing a contractionv. About the same time that an AP is produced Rt. Atrium will contract.vi. After 50msec, the SA node will send an electrical signal to the AV node which will delay the AP by .100msec.vii. The AP will travel to the AV branches, Purkinje Fibersviii. Ventricles will depolarize after 200msec.ix. Both ventricles will contract almost simultaneously.

Cardiac Cycle

1 complete contraction and relaxation of all 4 heart chambersi. Propels blood through circuitsii. Short term changes to BPiii. Forms heart sounds as blood pumps

Sounds of the Heart

1. S1- "Lubb" - long sound2. S2 - "Dubb"- short sharp sound3. S3 - galloping effect on sound due to extra-systole, common in children

a. Ventricles are in diastole and are not expanded therefore no blood flowb. Semilunar valves will prevent any backflow that usually occurs when the ventricles are in diastolei. S2 sound occurs- blood rebounding off of semilunar valveii. Quiescent Period:d. then ventricular filling may begin again5. Full cardiac cycle occurs for a total of 0.8sec /60sec. = 75bpm

Stroke Volume

amount of blood that is ejected from the ventricles, approx. 70mL in textbook case

End Systolic Volume

amount of blood left in ventricle after systole (both ventricles)i. Usually about 60mLii. EVS= EDV-SV (60mL = 130mL-70mL)

1. Pressure in arteries affect volume ejection2. Volumetric pressure needs to be the same in both circuits to prevent backflow and buildup3. Fluid will usually accumulate in the circuit that doesn't work4. There is a disruption to homeostasis

Congestive Heart Failure

one side works harder than the other.i. Caused by weakened heart muscle from heart disease, injury, infection, etc.1. Valvular insufficiencies2. Chronic Hypertension3. Congenital Deficienciesa. Dropsy 3. Aneurisms4. Kidney failure5. Heart failure - leads to strokeiv. Progressive condition where one side will affect the otherv. Irreversiblevi. Management can be done but there is no cure.

enlarged liver, swelling of fingers, ankles, and feet, distension of jugular vein, and build-up of fluid in abdominal cavity.

Cardiac Output

amount of blood ejected by each ventricle in 1 minutea. CO=SV*HRi. =75mL*75BPMii. = 5,250mL/min - resting COb. 4-6L of blood in each complete cycle c. Max CO = 21mL in healthy adult, and 35mL in Olympic trained athleted. Heart contains a Cardiac Reservei. The closer the cardiac reserve is to CO the less apt a person is for physical activityii. Large CR is better equipped for exercise